Arylene polyphosphate esters such as bisphenol-A bis(diphenylphosphate) are useful as flame retardants for various polymeric materials. Reported methods for their preparation typically involve reacting a diphenolic compound such as bisphenol-A with a diarylphosphoryl halide such as diphenylphosphoryl chloride. In such synthesis operations the product as produced is associated with various impurities such as unreacted starting material, partially phosphorylated product, acidic impurities, color bodies, and/or catalyst residues. Washing procedures that have been used to remove such impurities are of ten plagued by the formation of emulsions. See for example, U.S. Pat. Nos. 3,254,973; 5,420,327; and 5,756,798; and WO 98/35970, published Aug. 20, 1998.
The purification of bisphenol-A bis(diphenylphosphate) is complicated by the fact that not only is there the possibility of emulsion formation but in addition, during washing procedures product losses due to hydrolytic degradation can occur. Emulsions, even if formed sporadically, can consume considerable time and effort in effectively dealing with them. Hydrolytic degradation, if experienced, cannot be undone; product loss is inevitable. Moreover, crude bisphenol-A bis(diphenylphosphate) as formed is a viscous liquid and thus the removal of impurities from impure or crude bisphenol-A bis(diphenylphosphate) reaction product is not an easy proposition. Thus the provision of an effective way of reducing or preventing the formation of emulsions and of suppressing hydrolysis during the purification of impure bisphenol-A bis(diphenylphosphate) would be of considerable advantage.
This invention is deemed to provide an effective and efficient way of reducing or preventing the formation of emulsions and of suppressing hydrolysis during the purification of impure bisphenol-A bis(diphenylphosphate). The process technology of this invention is readily adaptable for use on an industrial scale, and is deemed independent of the particular process technology used in forming the impure product. Moreover, the process technology does not require large capital investments or involve excessive operating costs.
In one of its embodiments this invention is a process of minimizing or preventing emulsion formation and suppressing hydrolytic product degradation during the purification of an impure bisphenol-A bis(diphenylphosphate) product, which process comprises:
a) mixing such impure product with a liquid hydrocarbon solvent comprising at least one aromatic hydrocarbon and at least one paraffinic hydrocarbon in proportions of such impure product to such liquid hydrocarbon solvent in the range of about 25:75 to about 75:25 to form a hydrocarbon solution;
b) washing hydrocarbon solution from a) one or more times with an aqueous alkaline washing solution that has a specific gravity that differs from the specific gravity of the hydrocarbon solution by at least about 0.05 gram per cubic centimeter, after each such washing having the washed mixture settle into a purified organic phase and a separate aqueous phase, and separating these phases from each other, each such washing and separating being performed with the phases at a temperature in the range of about 25 to about 100xc2x0 C.; and
c) after completing the one or more washings and separations in b), washing the resultant purified organic phase one or more times with water to remove alkaline components from the hydrocarbon solution, after each such washing having the washed mixture settle into a less alkaline purified organic phase and a separate aqueous phase, and separating these phases from each other, each such washing and separating being performed with the phases at a temperature in the range of about 25 to about 100xc2x0 C.
The paraffinic hydrocarbon(s) used in forming the liquid hydrocarbon solvents employed in the practice of this invention can be (i) one or more cyclic paraffinic hydrocarbons (i.e., at least one cycloparaffinic hydrocarbon), (ii) one or more acyclic paraffinic hydrocarbons, or (iii) a mixture of (i) and (ii).
In preferred embodiments this invention is a process of minimizing or preventing emulsion formation and suppressing hydrolytic product degradation during the purification of an impure bisphenol-A bis(diphenylphosphate) product, which process comprises:
1) mixing (i) an aqueous buffer solution, or a dilute acid wash, or a water wash, the pH of any of which is less than about 5.5, with (ii) the impure product in the presence of a liquid hydrocarbon solvent comprising at least one aromatic hydrocarbon and at least one paraffinic hydrocarbon in proportions of impure product to such liquid hydrocarbon solvent in the range of about 25:75 to about 75:25, and then having the mixture settle into an organic phase and a separate aqueous phase, and separating these phases from each other;
2) washing organic phase from 1) one or more times with an aqueous alkaline washing solution that has a specific gravity that differs from the specific gravity of the organic phase by at least about 0.05 gram per cubic centimeter, after each such washing having the washed mixture settle into a purified organic phase and a separate aqueous phase, and separating these phases from each other, each such washing and separating in 2) being performed with the phases at a temperature in the range of about 25 to about 100xc2x0 C.; and
3) after completing the one or more washings and separations in 2), washing the resultant purified organic phase one or more times with water to remove alkaline components from the hydrocarbon solution, after each such washing having the washed mixture settle into a less alkaline purified organic phase and a separate aqueous phase, and separating these phases from each other, each such washing and separating in 3) being performed with the phases at a temperature in the range of about 25 to about 100xc2x0 C.
If in the above embodiments there are solids present in the solution formed either in a) or in 1), these can be separated as by filtration, decantation, or centrifugation. Although the number of times each of b) and c) above, or each of 2) and 3) above, is conducted depends on various factors such as the scale of operation and the relative quantities of aqueous washing liquids to organic phase, in a plant scale operation b) above or 2) above will typically be conducted twice, and c) above or 3) above will typically be conducted from two to three times as needed to suitably remove the alkaline residues from the purified product. When conducting b) above or 2) above at least twice, it is preferred that the concentration of the base such as sodium hydroxide in the first alkaline washing solution be higher than in the ensuing alkaline washing solution(s).
In the practice of the above embodiments, the times required in b) and c) above, or in 2) and 3) above, for the phases to separate and settle is typically quite short. For example, on a one-liter scale, each such separation and settling into separate liquid phases can occur in as little as about 1 to 2 minutes after agitation has been terminated.
If it is desired to isolate the purified bisphenol-A bis(diphenylphosphate) product, the final organic phase from c) above or 3) above is treated to remove the organic solvent. This can be readily accomplished either in vacuo and/or by removing the solvent(s) by azeotropic or steam distillation.
In particularly preferred embodiments, the organic solvent used is a mixture comprising in the range of about 10 to about 70 wt % of toluene, and in the range of about 10 to about 70 wt % of at least one liquid cycloparaffinic hydrocarbon, most preferably cyclohexane or methylcyclohexane, or both, with the total of these components being at least 90 wt %, with the balance, if any, to 100% being at least one other aromatic hydrocarbon. An especially preferred organic solvent is a liquid mixture consisting essentially of (i) toluene and (ii) cyclohexane or methylcyclohexane, or both, in a weight ratio of (i):(ii) in the range of about 30:70 to about 70:30. It is also particularly preferred to employ as the aqueous alkaline washing solution, an aqueous alkali metal hydroxide solution, and especially an aqueous sodium hydroxide solution.
The above and other features and embodiments of this invention will be still further apparent from the ensuing description and appended claims.
Bisphenol-A bis(diphenylphosphate) which can be effectively purified by use of this invention can be represented by the formula
(PhO)2P(xe2x95x90O)O[C6H4C(CH3)2C6H4OP(xe2x95x90O)(OPh)O]nPh
where Ph is phenyl, C6H4 is a p-phenylene group, and n is a number in the range of 0 to about 5 with the provisos that (A) if the depicted phosphate is a single compound, then n is 1, 2, 3, 4, or 5, and (B) if the depicted phosphate is a mixture of such depicted phosphate esters in which the numerical values for n are not the same for each molecule of the mixture, then n can (but need not) include zero, and is the average number for such mixture and is in the range of about 1 to below 5, preferably is between 1 and about 2, and most preferably is between 1 and about 1.5. That is, where the product to be purified is a mixture, some triphenylphosphate can be present along with compounds of the above formula where n is, for example, 1, 2 and 3. In addition, at least 90 wt % of the balance, if any, to 100 wt % is composed of other phosphorus-containing species.
A preferred product formed by use of the process of this invention consists essentially of at least about 78-87 wt % of compound of the above formula where n is 1; at least about 11-12 wt % of compound of the above formula where n is 2; at least about 1 to about 1.5 wt % of compound of the above formula where n is 3; about 0-1.5 wt % of compound of the above formula where n is zero (i.e., triphenylphosphate); and at least 90 wt % of the balance, if any, to 100 wt % being other phosphorus-containing species. These are excellent flame retardant compositions.
As an example of the efficiency of the process technology of this invention, it has been found possible to convert a crude bisphenol-A bis(diphenylphosphate) reaction product comprised of about 69.5 wt % of compound of the above formula where n is 1, into a product of this invention consisting essentially of 84.66 wt % of compound of the above formula where n is 1; 11.99 wt % of compound of the above formula where n is 2; 1.46 wt % of compound of the above formula where n is 3; less than 100 ppm of isopropenylphenyl diphenylphosphate; 0.11 wt % of bisphenol-A mono(diphenylphosphate); and 0.27 wt % of diphenylphosphate, with at least 90 wt % of the balance to 100 wt % being other phosphorus-containing species.
This invention is applicable to the purification of bisphenol-A bis(diphenylphosphate) produced by any of a variety of synthesis procedures, such as procedures of the types described, for example, in U.S. Pat. Nos. 2,520,090; 3,254,973; 4,343,732; 5,281,741; 5,420,327; or 5,756,798; or in WO 96/13508; or WO 96/17853; or in Japan Kokai Nos. 51/103195 A2; 51/174331 A2; 59/202240 A2; 63/227632 A2; or 05/186681 A2. The important thing is that the impure or crude product has associated with it one, or typically more than one, impurity such as one or more acid impurities, color bodies, unreacted starting materials, partially phosphorylated intermediates, residual catalyst, catalyst residues, halide impurities, or the like. In this connection, the words xe2x80x9cimpurexe2x80x9d and xe2x80x9ccrudexe2x80x9d are used interchangeably in this document to denote that the product being purified contains one or more such impurities.
It is preferred that the impure or crude product mixture not be subjected to an alkaline wash prior to conducting a) or 1) above. Such a wash tends to engender reaction of the base with any phenolic species present as impurities to thereby form products having surfactant properties. This in turn can cause a hydrolysis and/or an emulsion to form. Instead, it is preferable to subject the impure or crude product mixture to one or more washings with water, or with an aqueous buffer solution having a pH of less than about 5. This is accomplished by thoroughly mixing (i) an aqueous buffer solution with a pH of less than about 5, or water with (ii) the impure or crude product mixture in the presence of the liquid hydrocarbon solvent comprising at least one aromatic hydrocarbon and at least one paraffinic hydrocarbon in proportions of impure product mixture to such liquid hydrocarbon solvent in the range of about 25:75 to about 75:25, and then having the mixture settle into an organic phase and a separate aqueous phase, and separating these phases from each other. Thereafter 2) and 3) above are, of course, carried out. Some of the advantages of using such water wash or aqueous buffer wash in the process include:
1) Fast phase separation of the organic layer containing the washed crude product and the aqueous layer from such washing which contains catalyst residues and phosphoric acid-type impurities.
2) Virtual elimination of emulsion formation that would require reworking which is both time-consuming and costly.
3) Cycle time in the overall process is greatly improved and thus manufacturing cost is reduced.
4) At most, only low levels of metal impurities are present in the final purified product.
5) Further reductions in phenolic impurities in the final purified product can be achieved.
6) Final product with a low acid number can be produced.
While various aqueous buffer solutions with pH below about 5.5 can be used as the washing solution, use of aqueous phosphate-containing buffer solution with pH below about 5.5 are preferred. Use of an aqueous buffer solution is desirable when performing the washing in vessels susceptible to corrosion by contact with acidic liquid media. Among suitable dilute acid washes with pH below about 5.5 that can be used are mineral acids, water-soluble organic acids, and acidic salts. A few examples include hydrochloric acid, sulfuric acid, phosphoric acid, methanesulfonic acid, and sodium dihydrogen phosphate. Dilute sulfuric acid is one of the preferred dilute acid washes. A typical water wash with a pH below about 5.5 is water containing dissolved carbon dioxide, ie., carbonated water.
The amount of aqueous buffer solution, dilute acid wash, or water wash used in the initial aqueous buffer wash, dilute acid wash or water wash is not critical as long as enough of such wash is used to carry out an effective washing operation. Minimally, at least about 5-10 pounds of the buffer wash solution, dilute acid wash, or water wash can be used per each 100 pounds of the crude or impure product. Desirably, the ratio of the buffer wash, dilute acid wash, or water wash to the crude or impure product will be higher than this. For example, ratios in the range of up to at least about 20-50 pounds of the wash per each 100 pounds of crude or impure product can be used.
In conducting this optional, but preferred, initial aqueous buffer wash, or dilute acid wash, or water wash it is important to ensure that any substantial amount of the wash does not come in contact with the crude or impure product mixture in the absence of hydrocarbon solvent. Thus one suitable feeding procedure is to feed the wash being used into the washing vessel after the hydrocarbon solvent and the crude or impure product mixture have been charged into the vessel and mixed together, e.g., by charging these components in the following order: 1) hydrocarbon solvent, 2) crude or impure product mixture, and 3) aqueous buffer wash, or dilute acid wash, or water wash. Another suitable feeding procedure for this optional, but preferred, initial washing operation is to feed the crude or impure product mixture into the vessel which already contains the wash being used and the hydrocarbon solvent. As noted above the hydrocarbon solvent used comprises at least one aromatic hydrocarbon and at least one paraffinic hydrocarbon. Other feasible ways of feeding hydrocarbon solvent, crude or impure product mixture, and aqueous buffer wash, or dilute acid wash, or water wash may be used provided that the performance of the process in minimizing or preventing emulsion formation and suppressing hydrolytic product degradation during the purification is not materially interfered with.
Mixed liquid hydrocarbon solvents used in the practice of this invention comprise at least one aromatic hydrocarbon and at least one paraffinic hydrocarbon. It is not essential that each component making up the solvent mixture be a liquid at 20xc2x0 C. provided the mixture itself is in the liquid state at 20xc2x0 C. Preferably however each of the components of the solvent mixture is a liquid at 20xc2x0 C. Typically the mixture will comprise at least 50 wt %, and preferably at least 65 wt % of the combination of aromatic and paraffinic hydrocarbon components. The balance, if any, can be one or more other suitable non-polar or essentially non-polar solvent components, such as olefinic or cycloolefinic hydrocarbons (e.g., one or more isomeric forms of hexene, heptene, octene, nonene, decene, undecene, dodecene, cyclopentene, cyclohexene, methylcyclohexene or the like, or mixtures of any two or more of olefinic and/or cycloolefinic hydrocarbons such as the foregoing. The relative proportions of aromatic hydrocarbon to paraffinic hydrocarbon will depend on such factors as the target specific gravity of the solution to be formed in a) or 1) above, the specific gravity of the aqueous alkaline solution being used in b) or 2) above, and, of course, the specific gravities of the aromatic and paraffinic components themselves. Thus in any given situation where the appropriate relative proportions of the aromatic and paraffinic components has not been previously ascertained, a few pilot experiments should be conducted to develop the appropriate relative proportions.
Examples of suitable aromatic hydrocarbons for use in forming the mixed aromatic-paraffinic hydrocarbon solvent composition include benzene, toluene, xylene, ethylbenzene, propylbenzene, cumene, isobutylbenzene, isohexylbenzene, amylbenzene, tert-amylbenzene, pentaethylbenzene, 1-methylnaphthalene, 1,2,3,4-tetrahydronaphthalene and analogous aromatic hydrocarbons, which typically contain up to about 18 carbon atoms in the molecule, but which may contain any number of carbon atoms as long as the resultant mixed aromatic-paraffinic solvent composition is a free-flowing liquid at the temperature at which the mixed solvent composition is employed.
Cycloparaffinic hydrocarbons suitable for use in forming the mixed aromatic-paraffinic hydrocarbon solvent composition include cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, 1,3-dimethylcyclohexane, 1,4-dimethylcyclohexane, isopropylcyclohexane, p-menthane, 1,3,5-trimethylcyclohexane, and analogous cycloparaffinic hydrocarbons, which typically contain up to about 14-16 carbon atoms in the molecule. However, the cycloparaffinic hydrocarbon(s) may contain any number of carbon atoms as long as the resultant mixed aromatic-paraffinic solvent composition is a free-flowing liquid at the temperature at which the mixed hydrocarbon solvent composition is employed.
Acyclic paraffinic hydrocarbons suitable for use in forming the mixed aromatic-paraffinic hydrocarbon solvent composition include, for example, such compounds as any of the isomeric forms of pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, and their higher homologs. Typically these hydrocarbons contain up to about 14-16 carbon atoms in the molecule, but they may contain any number of carbon atoms as long as the resultant mixed aromatic-paraffinic hydrocarbon solvent composition is a free-flowing liquid at the temperature at which the mixed solvent composition is employed.
Preferred mixed aromatic-paraffinic hydrocarbon solvent mixtures are free-flowing liquid mixtures composed of (A) one or more aromatic hydrocarbons and one or more cycloparaffinic hydrocarbons, or (B) one or more aromatic hydrocarbons, one or more cycloparaffinic hydrocarbons, and one or more acyclic paraffinic hydrocarbons, in which at least 50 wt % of the paraffinic portion of the aromatic-paraffinic hydrocarbon mixture is one or more cycloparaffinic hydrocarbons.
Preferably the aromatic-paraffinic hydrocarbon solvent mixture should be a composition that will distill, either azeotropically or with the aid of steam and/or vacuum, at a temperature below about 160xc2x0 C., and more preferably below about 130xc2x0 C.
A more preferred solvent mixture is a liquid mixture comprising in the range of about 10 to about 70 wt % percent of at least one aromatic hydrocarbon and in the range of about 10 to about 70 wt % percent of at least one cycloparaffinic hydrocarbon, with the total of these components being at least 90 wt % and preferably 100 wt % of the hydrocarbon mixture. A still more preferred liquid solvent mixture is comprises in the range of about 10 to about 70 wt % percent of toluene and in the range of about 10 to about 70 wt % percent of at least one cycloparaffinic hydrocarbon, with the total of these components being at least 90 wt %, with the balance, if any, to 100% being at least one other aromatic hydrocarbon. Particularly preferred is a liquid mixture consisting essentially of (i) toluene and (ii) cyclohexane or methylcyclohexane, or both, in a weight ratio of (i):(ii) in the range of about 30:70 to about 70:30.
It is within the purview of this invention to include non-hydrocarbonaceous components in the mixed aromatic-paraffinic hydrocarbon solvent mixture as long as such components do not in any way detract from the performance of the mixed solvent composition. The inclusion of such components, although permissible, is not recommended.
To minimize the risk of emulsion formation, the entire quantity of the crude product mixture should be dissolved in the hydrocarbon solvent mixture before initiating the washing step(s) using an aqueous alkaline washing solution. Better still, the entire quantity of the crude product should be washed with water or an aqueous buffer solution in the presence of the hydrocarbon solvent mixture in the manner described above before initiating the step(s) of washing the hydrocarbon solution of the product mixture with an aqueous alkaline washing solution. If any of the crude product remains undissolved in the hydrocarbon solvent mixture, there is a distinct possibility that excessive amounts of emulsions may be formed during such alkaline washing step, and thus such undissolved material should be removed. Preferably, the solution of the crude product in the hydrocarbon solvent mixture should have a solvent loading (i.e., the solution should contain) in the range of about 25 to about 75 wt % of completely dissolved crude product as a homogeneous solution. Any solids in the solution are preferably removed by filtration or the like.
The aqueous alkaline washing solution used in b) or 2) above contains inorganic base in solution, typically an inorganic base of an alkali metal or an alkaline earth metal, or both. Examples of suitable bases which can be used in forming the aqueous washing solution include lithium oxide, sodium oxide, potassium oxide, lithium hydroxide, sodium hydroxide, potassium hydroxide, potassium carbonate, barium oxide, barium hydroxide, and similar compounds. Of these, the alkali metal oxides are preferred starting materials as they form hydroxides in water, and the alkali metal hydroxides, especially potassium hydroxide and most especially sodium hydroxide, are particularly preferred starting materials. Other suitable inorganic bases such as ammonia or ammonium hydroxide maybe used. Usually the washing solution used in b) or 2) above has dissolved therein approximately 0.1-15 wt % of alkali metal oxide, hydroxide, or carbonate, or the corresponding molar equivalent of other suitable base. Aqueous solutions in the range of about 0.1 to about 15 wt % of sodium hydroxide are highly suitable because of their excellent effectiveness and low cost.
The washing operation(s) in b) or 2) above are typically performed at one or more temperatures in the range of about 25 and about 100xc2x0 C., and preferably in the range of about 45 and about 75xc2x0 C. In addition, it is preferred to coordinate (i) the solvent loading of the solution of crude produce in the hydrocarbon solvent mixture, with (ii) the wash operating temperature(s) being used. Proper coordination of these variables can significantly reduce the possibility of problems arising with respect to solubility and/or emulsion formation during the washing operations of b) above or 2) above. For example, when using a 42% loading of crude bisphenol-A bis(diphenylphosphate) in a mixed hydrocarbon solvent of this invention, the washing temperature should be kept above about 40xc2x0 C. in order to prevent problems with solubility and the emulsions which result. Solvent loadings above 42 wt % enable the washing operations to be conducted at progressively lower wash operating temperatures without incurring solubility or emulsion problems. In any given situation where optimal coordinated solvent loading and washing temperature conditions have not been previously ascertained, it is a simple matter to perform a few preliminary tests to ascertain optimal coordinated conditions for use in such situation.
Mixing in c) or 3) above should be of sufficient intensity and duration to ensure thorough contact between and among the components. The mixture should thus be agitated by suitable stirring means or shaking means such as, for example, a mechanical stirrer or a mechanical shaker. Mixing is typically conducted with the mixture at a temperature in the range of about 25 to about 100xc2x0 C., and preferably in the range of about 45 to about 75xc2x0 C.
After the mixing in c) or 3) above, the mixture is allowed to settle while in a quiescent state whereby the organic and aqueous phases separate into two distinct layers. If the operation is properly conducted there will be little if any rag between the phases. Thereafter the phases can be separated from each other by draining or decanting one phase layer from the other. Usually, and preferably, the organic layer will be superposed on the underlying aqueous layer thus enabling the aqueous layer with the impurities therein to be drained from the washing vessel. This enables the purified bisphenol-A bis(diphenylphosphate) to be recovered from the organic solution by vaporizing or distilling off the solvent without transferring the solution from the mixing vessel. The vaporized solvent is preferably condensed and collected for reuse in the process.
Preferably, the purified bisphenol-A bis(diphenylphosphate) and the hydrocarbon solvents are separated by use of in situ or live steam stripping for efficient removal of the hydrocarbon solvents used as the organic medium for the alkaline washes. For this purpose an external supply of steam can be introduced into the solution or water can be added to the solution and the resultant mixture heated to generate the steam in situ. A vacuum is typically applied to expedite this stripping operation. The use or in situ generation of steam allows the solvent strip to be performed in less processing time, e.g., two hours versus 12 hours for standard flash at the same operating temperature. Also, use or in situ generation of steam enables the separation to be performed at lower temperatures (e.g., about 35 to about 130xc2x0 C., and/or higher pressures (e.g., about 0 to about 100 mm Hg absolute). Use of such lower temperatures minimizes product degradation caused by use of higher temperatures and eliminates the need for more costly vacuum equipment (e.g., vacuum pumps and/or wiped film evaporators).
It is also preferred to conduct the process operations of this invention in an inert environment, such as under a nitrogen blanket or blanket of other inert gas such as argon. By operating in this manner, haze formation or development of turbidity can be minimized, if not eliminated.
When the process technology of this invention is properly conducted, the competing reaction of hydrolysis of bisphenol-A bis(diphenylphosphate) is suppressed, even when separating the solvent from the purified bisphenol-A bis(diphenylphosphate) by steam distillation. Hence yield losses due to hydrolysis of the bisphenol-A bis(diphenylphosphate) during the entire purification operation are minimal. Without desiring to be bound by theory, it is believed that the suppression of hydrolysis during the washing step and, in the most severe case, during steam distillation is due to the low polarity of solvent mixture.
The following illustrative Examples are not intended to limit, and should not be construed as limiting, the generic scope of this invention. Example I-V are for comparative purposes. Examples VI-XV illustrate the invention. In these Examples all percentages are by weight, and the following acronyms are used:
BPADP is bisphenol-A bis(diphenylphosphate);
BPA is bisphenol-A;
TPP is triphenylphosphate;
IPP is isopropenylphenyl diphenylphosphate; and
DPP is diphenylphosphate.
References to n are to the number of repeating moieties in the oligomers, such number being designated as n in the formula presented hereinabove.